As the supply of oil becomes more scarce, exploration and production activities are increasingly being performed at offshore locations. Attempts to recover offshore oil deposits for commercial use give rise to the possibility that accidental leaks may contaminate our oceans. Further possibilities for oil pollution arise during transportation of crude oil from its deposit location to the refinery or other destination.
To be effective, removal of oil from an oil spill must be rapid. As time elapses, spilled oil becomes more difficult to collect. It spreads rapidly and undergoes changes with time, rendering the oil more dense. The weathering of the oil is related to the condition of the surrounding sea, temperature and oil type. Should spilled oil reach the shore, ecological damage and restoration costs increase astronomically.
Methods for removing hydrocarbon liquids and restoring the quality of the water to desired characteristics include the use of chemical additives to cause a change in the characteristics of the oil; the use of various materials to absorb the oil from the water; and the use of confining devices and pumps to prevent the spread of oil and remove the oil from the surface of the water.
There are three major types of confining devices presently used to recover pollutants floating on a body of water. The first type is a weir-type skimmer, supported on the body of water, that permits the uppermost surface of the body of water to flow into a sump, from which the accumulated liquid is pumped to a separating tank located aboard a floating vessel. The second type is a floating suction skimmer that sucks the upper surface of the water into a separating tank. The third type is an absorbent surface skimmer, combining the characteristics of both absorbent materials and confining devices. The typical absorbent surface skimmer includes a rotating absorbent belt removing oil from the water surface and depositing it in a collection pan.
Present weir-type skimmers share at least one of the following inadequacies: inability to operate effectively in other than substantially calm waters, inability to recover oil at rates desirable for a major spill, and inability to be deployed quickly because of size and weight. The first inadequacy is the most common of existing weir-type skimmers. As wave heights increase, the oil-to-water recovery rate decreases. The increased water intake is due to the inability of the skimmer to conform to the sea surface.
The second inadequacy, low oil recovery rates, is due, in part, to the problem of wave heights, previously discussed, and also to design restrictions and deficiencies. A skimmer must be able to provide high volume flow rates for oil slicks of different depths. The recovery device should be able to operate effectively in both very thin and very thick oil slicks and be capable of adjusting output relative to the amount of oil recovered.
The last inadequacy concerns deployment of the skimmer. Storage, transport and operation of the skimmer become increasingly difficult with size and weight gains.
The present invention provides a method and means for collecting an immiscible liquid from the surface of a body of higher density liquid which is not subject to the deficiencies of the prior art.